Contemporary state and perspectives of the reflection research are analyzed. The necessity of differentiation of general subject of reflection psychology is founded as the main requirement for successful research: reflection should be studied as synthetic mental reality that differentiates into three major aspects — mental process, mental property and mental state. There is presented and substantiated the author’s inventory used to diagnose the individual level of reflectiveness development. The empirical data demonstrating the dependence between the level of reflectiveness and result parameters as well as process and style parameters are discussed. There were found and interpreted new laws of reflection determination of mental properties and personal traits structure.